Control of current in electrolytic apparatus



Aug. 19, 1969 J. A. WALLINDER 3,462,356

CONTROL OF CURRENT IN ELECTROLYTIC APPARATUS 7 Filed Oct. 14, 1964 2 Sheets-Sheet 1 191mm? Jo 1r: A, Wa Hinder Aug. 19, 196 9 J, WALUNDER I 3,462,356

CONTROL OF CURRENT IN ELECTROLYTIC APPARATUS Filed Oct. 14, 1964 2 Sheets-Sheet; 2

J Job 4. Wal/[nder mw- I I United States Patent Ofitice 3,452,356 Patented Aug. 19, 1969 U.S. Cl. 204-228 3 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to means for controlling electric current in electrolytic apparatus. The apparatus is provided with a current-controlling means having a device connected with the electrolytic apparatus, which currentcontrolling device is in position to be contacted by gas evolved by the electrolysis in said apparatus; said. device being responsive to hydrogen concentration in said'gas by reason of the high thermal conductivity of hydrogen, the said device comprising an electrically resistive element having an appreciable coeflicient of resistance and is connected with said current controlling means, so that when said device is contacted by hydrogen in concentration, the resistance of said element will change due to the high thermal conductivity of the hydrogen, said change of resistance being operative to control the current in said electrolytic apparatus.

This invention concerns improvements relating to the control of electric current in electrolytic apparatus such as plating baths and cells or batteries of the secondary type. The invention seeks to provide a simple but sensitive arrangement by which the current can be varied in response to the occurrence of electrolysis and/or in relation with the electrolysis which occurs.

The current employed in an electrolytic process is frequently required to be the maximum current which will produce no gassing or only a predetermined amount of gassing. Detection of gassing by monitoring the at tainment of a gassing voltage has shortcomings, due principally to variations of the voltage at which gassing occurs caused by changes of temperature and in the chemical consistency of the electrolyte. An object of the invention is to avoid these shortcomings.

According to the invention, a resistive element which is connected to or associated with means for controlling the current in the electrolytic apparatus is disposed in or on the apparatus in a position where it will be contacted by hydrogen gas evolved by electrolysis occurring in the said apparatus.

Hydrogen has a far higher thermal conductivity than the oxygen and nitrogen of the air. Consequently a resistive component carrying a regulated current and attaining a certain constant temperature rise, dependent upon its suface area and upon the energy supplied, above the ambient temperature when in normal air will attain a different temperature rise in the presence of hydrogen. The conductivity of the medium surrounding the element will be greater and the temperature of the element will be less. The temperature change, which is directly dependent upon the evolution of the hydrogen in the electrolysis can therefore be utilised as the operative factor for controlling the current in the electrolytic apparatus in response to the occurrence of gassing.

If the resistive element has an appreciable temperature coefiicient of resistance, the change in its resistance upon variation of its temperature may be used for producing the required control. The said element may be connected in a bridge or other comparison circuit whose output is supplied, generally by way of an amplifier, to the means for controlling the current in the electrolytic apparatus. However, the temperature change may itself be detected or measured and used for bringing about the required regulation.

Provision may be made for compensating for or balancing out the effect, upon the resistive element, of variation of ambient temperature, for example in the comparison circuit.

One manner of carrying the invention into effect will now be more fully described by way of example and with reference to the accompanying drawings, in which:

FIGURE 1 is a circuit diagram,

FIGURE 2 a longitudinal section, on the line 11-11 in FIGURE 3, through a hydrogen-detecting probe, and

FIGURE 3 an exploded perspective view of the probe.

The circuit and probe to be described have been devised more particularly for use in the control of the charging of a secondary battery of the lead-acid or nickel-cadmium type in dependence upon the evolution of hydrogen by electrolysis in one of the cells.

As far as the circuit diagram of FIGURE 1 is concerned, the probe 1 to be placed in communication with the said cell so as to be exposed to hydrogen evolved therein comprises two resistors 2, 3 connected in series. A constant direct current supplied to the resistors 2, 3 is derived from an AC. source 4 by Way of a transformer 5, one or more barretters 6, a current. transformer 7, a rectifying bridge 8 and smoothing capacitor 9.

The battery, connected to the terminals 10, is charged with rectified current derived from the AC. source 4 by way of a barretter 11, a transistor 12, a rectifying bridge 1 3and a series regulator comprising a transistor 14. The transistor 14 is controlled by way of an amplifier, comprising transistors 15, 16, which is also supplied through the transformer 12 by way of rectifiers 17 and a Zener diode 18.

The resistors 2, 3 form two adjacent arms of a resistance bridge circuit whose other arms are formed by resistors 19, 20 of constant value. As illustrated, provision is made for initial bridge adjustment, but thereafter the ratio of the resistances of the said other arms remains fixed. The output of this bridge circuit is applied between the base and emitter of the first transistor 15 of the amplifier.

The resistors 2, 3 are thermistors, that is they have a considerable, negative, temperature coetficient of electrical resistance. For the purposes of explanation, it will be assumed first of all that the resistors 2, 3 have unequal resistances when carrying the regulated current in air and that only the resistor 2 is exposed to the hydrogen, when evolved, whereas the resistor 3 is always in air. As long as no hydrogen is evolved, or the evolution of hydrogen is below a predetermined low limit, the temperatures attained by the resistors 2, 3 due to the same current flowing through them will be the same, their resistances will remain unequal, the bridge circuit 2, 3, 19, 20 will remain unbalanced and, due to the output signal from the said circuit, the amplifier 15, 16 will be inoperative for producing reduction of the charging current by the transistor 14. The battery will be supplied with the maximum charging current. If, however, hydrogen is evolved, the temperature of the resistor 2 will be reduced, the bridge circuit will tend to become balanced and the elimination of the output signal applied to the transistor 14 will produce a regulating action which will reduce the charging current until the evolution of hydrogen is suppressed. Since the two resistors 2 and 3 are equally affected by ambient temperature, variations in the latter will cause variation of output signal from the bridge circuit.

The arrangement just described is indeed a practical arrangement and can be employed. It is, however, preferred to expose both resistors to the hydrogen evolved and to select thermistors having materially different resistances when cold, i.e. at normal temperatures. As the heat developed in a resistor is proportional to its resistance and as the two resistors 2, 3 carry the same current, the heat developed in the resistor of the higher resistance will be greater than that developed in the resistor of lower resistance. However, the cooling effect of hydrogen is the greater the greater the difference in temperature between the hydrogen and the resistor. Consequently the hotter resistor with the higher resistance will lose more heat than the cooler resistor when hydrogen is evolved, so that their temperatures are differently reduced and the temperature difference between them becomes less. Therefore, if the bridge circuit was unbalanced with the resistors 2, 3 in air, it will tend to become balanced when the resistors are differently cooled by hydrogen and the elimination of the output signal will then initiate reduction of the charging current as described above. On the other hand, changes in ambient temperature will again affect both resistors equally and no variation of output signal will be produced by such changes.

Naturally, the inverse arrangement can be employed, that is the bridge circuit may be arranged to be balanced as long as no hydrogen is evolved and to become unbalanced upon the evolution of hydrogen. However, the arrangement described above is preferred as it has a failsafe action in the event of a fault in the bridge circuit.

In place of resistors with a negative temperature coefficient of resistance, use may be made of resistors with a positive coefficient, composed for example of nickel wire.

Instead of using a resistor or resistors exposed to the evolved hydrogen directly to produce an output signal, it or they may be indirectly coupled to or act thermally upon some other device responsive to temperature change, for example a thermo-couple or a temperaturesensitive resistor or switching device.

Arrangements such as have been described above may be similarly applied to regulate the current supplied to a plating bath or like apparatus.

Other known circuits or devices may be employed for regulating the supply of current for the electrolytic apparatus, for example such comprising thyratrons or other thermionic valves, other arrangements of transistors or silicon controlled rectifiers or magnetic amplifiers, or combinations of such components, if required in conjunction with Zener diodes or gas-discharge tubes as reference-voltage devices or regulators for the values of currents or voltages in control circuits.

In any case in which an indication of the presence of hydrogen is required instead of or in addition to a control action, the output of the bridge circuit may be supplied, possibly after amplification, to an indicating instrument or a visual or audible signal device.

Similar arrangements may also be used for detecting the presence in an atmosphere of a gas other than hydrogen having a thermal conductivity different from that of air and for producing an indication or control action in response thereto.

FIGURES 2 and 3 illustrate one form which the probe 1 may take. An outer capsule 21 is formed with a threaded spigot 22 which can be screwed into an opening, for instance filling opening, in the top of the cell. The capsule is closed by a tightly fitting cover 23 having a vent 24 or an outlet spigot 25', the latter for instance if evolved gases are to be carried away for recombination with the assistance of a catalyst. The resistors 2 and 3 coated with a thin protective medium are supported on the cover 23 from which a cable 26 containing their leads 27 is brought out through a spigot 28. The resistors 2 and 3 are further protected against electrolyte by a cup 29 fitted in the cover by means of a sealing ring 30 and divided by a transverse partition 31 which also prevents the temperature of one resistor from being directly affected by that of the other. As seen more clearly in FIGURE 3, the upper edge of the cup is cut away to afford communication with the spigot 25 and also to clear the supporting means for the resistors and the end of their cable 26. The compartments 32a, 32b formed in the cup by the partition 31 are in communication with the cell, by way of the spigot 22., through small openings 33 formed in the base of the cup 29 and masked by a disc-shaped baffle 34 which is arranged to leave a narrow annular gap at its periphery. If it was desired to expose one resistor, say the resistor 2, to hydrogen evolved, then only the opening 33a would be provided and the partition 31 would be arranged to separate the compartments 32a and 32b substantially completely. The compartment 3212 would be in communication with the outside air by way of the vent 24. The several parts 21, 23 and 29 of the probe may suitably be made of a synthetic plastic material.

I claim:

1. A system for controlling the amplitude of current applied to electrolytic apparatus comprising,

a source of current connected to the electrolytic apparatus,

means responsive to a control signal for varying the amplitude of current supplied by said source to said electrolytic apparatus,

and means for generating said control signal including two temperature responsive resistors, means for causing a regulated current to flow through both said resistors, said resistors being both disposed to be affected alike by the level of ambient temperature and both being exposed to substantially the same degree to any gas evolved by electrolysis in said electrolytic apparatus, said resistors having significantly different resistance values so as to be heated to correspondingly different temperatures by said regulated current, and means operatively connected to both said resistors for providing said control signal when hydrogen is evolved by said apparatus the hydrogen by reason of its greater thermal conductivity than air causing a greater cooling of the one of said two resistors which is at the higher temperature.

2. An arrangement as claimed in claim 1, wherein temperature-responsive means is provided for compensating for the effect, upon the said element, of variation of ambient temperature.

3. An arrangement as claimed in claim 1, wherein the apparatus is a secondary cell in which hydrogen 1s evolved on the occurrence of electrolysis and the current controlled is the charging current supplied to the said cell, a hydrogen-detecting probe comprising a capsule which is connected to the upper part of the cell and which contains compartments in which said resistors are disposed and which are equally readily accessible to hydrogen from the cell, but baffled against access by liquid electrolyte.

References Cited UNITED STATES PATENTS 3,325,378 6/1967 Greene et a1. 2.04-293 XR 2,578,027 12/1951 Tichenor 204-230 3,123,758 3/1964 Giacalone 320-36 JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner US. Cl. X.R. 320-31, 35 

